Low observable aircraft having tandem longitudinal lift fans

ABSTRACT

An aircraft operable to transition between thrust-borne lift in a VTOL orientation and wing-borne lift in a forward flight orientation. The aircraft has a blended wing body and includes first and second engines, a binary lift fan system, first and second forced air bypass systems and first and second exhaust systems. The engines have turboshaft and turbofan modes. The lift fan system includes ducted fans in a tandem longitudinal orientation. In the VTOL orientation of the aircraft, the engines are in the turboshaft mode coupled to the lift fan system such that the engines provide rotational energy to the ducted fans generating the thrust-borne lift. In the forward flight orientation of the aircraft, the engines are in the turbofan mode coupled to the forced air bypass systems such that the bypass air combines with the engine exhaust in the exhaust systems to provide forward thrust generating the wing-borne lift.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 63/001,286, filed Mar. 28, 2020, the entire contents ofwhich are hereby incorporated by reference.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to blended wing bodyaircraft having low observable characteristics and, in particular, toVTOL aircraft having a lift fan system generating thrust-borne lift, aforced air bypass system generating wing-borne lift and an active flowcontrol system generating control moments in both thrust-borne lift andwing-borne lift flight regimes.

BACKGROUND

Unmanned aerial vehicles or UAVs are self-powered aircraft that do notcarry a human operator, use aerodynamic forces to provide vehicle lift,are autonomously and/or remotely operated, may be expendable orrecoverable and may carry lethal or nonlethal payloads. UAVs arecommonly used in military applications such as intelligence,surveillance, reconnaissance and attack missions. Certain UAVs have thecapability of being networked together enabling cooperation with oneanother including, for example, exhibiting swarm behavior such as theability to dynamically adapt to changing conditions, group coordination,distributed control, distributed tactical group planning, distributedtactical group goals, distributed strategic group goals and/or fullyautonomous swarming. It has been found, however, that such highlycapable UAVs typically require runways for takeoff and landing orrequire specialized systems for launch and recovery.

Vertical takeoff and landing or VTOL aircraft are capable of taking offand landing vertically without the requirement of a runway. Rotorcraftsuch as helicopters, tiltrotors, tiltwings, quadcopters and othermulticopters are examples of VTOL aircraft. Each of these rotorcraftutilizes one or more open rotor disks to provide lift and thrust to theaircraft. Such open rotor disks not only enable vertical takeoff andlanding, but may also enable hover, forward flight, backward flight andlateral flight. These attributes make VTOL aircraft highly versatile foruse in congested, isolated or remote areas. It has been found, however,that the use of open rotor disks is a detriment to the radarcross-section of typical VTOL aircraft.

Low observable aircraft use a variety of technologies to reducereflection and emission of radar, infrared, visible light, radiofrequency spectrum and/or audio to avoid detection. While no aircraft istotally invisible to radar, low observable aircraft are more difficultto detect and track, thereby increasing the odds of successfullyavoiding detection by enemy radar and/or targeting by radar guidedweapons. Such low observable aircraft consequently provide the operatorwith an enhanced ability to penetrate integrated air defense systems.What is needed is a highly capable UAV that does not require a runwayfor takeoff and landing or specialized systems for launch and recovery,that is capable of vertical takeoff, hover, forward flight, backwardflight, lateral flight and vertical landing and that has low observableattributes.

SUMMARY

In an aspect, the present disclosure is directed to an aircraft operableto transition between thrust-borne lift in a VTOL orientation andwing-borne lift in a forward flight orientation. The aircraft includes ablended wing body having first and second engines disposed therein. Theengines have a turboshaft mode and a turbofan mode and are configured togenerate engine exhaust. A binary lift fan system is disposed within thebody and includes ducted fans in a tandem longitudinal orientation.First and second forced air bypass systems are disposed within the bodyand are configured to generate bypass air. A first exhaust system iscoupled to the first engine and the first forced air bypass system. Asecond exhaust system is coupled to the second engine and the secondforced air bypass system. In the VTOL orientation, the first and secondengines are in the turboshaft mode coupled to the lift fan system suchthat the first and second engines provide rotational energy to theducted fans generating the thrust-borne lift. In the forward flightorientation, the first and second engines are in the turbofan modecoupled to the first and second forced air bypass systems such that thebypass air combines with the engine exhaust in the respective first andsecond exhaust systems to provide forward thrust generating thewing-borne lift.

In certain embodiments, the blended wing body may include a fuselage anda wing. In some embodiments, the blended wing body may have a kiteshaped body with forward winglets. In certain embodiments, the ductedfans may each include a rotor assembly having a plurality of variablepitch rotor blades. In some embodiments, the tandem longitudinalorientation of the ducted fans may be configured to generate pitchcontrol moments in the VTOL orientation. In certain embodiments, eachforced air bypass system may include an inlet, a bypass fan disposedwithin the body downstream of the inlet and a bypass duct disposedwithin the body downstream of the bypass fan with the bypass ductcoupled to the respective exhaust system. In such embodiments, theinlets may be air inlets on an upper surface of the body. In someembodiments, each exhaust system may include a film cooled nozzle. Incertain embodiments, a transmission may be disposed between the enginesand the lift fan system such that the transmission engages the engineswith the lift fan system when the engines are in the turboshaft mode anddisengages the engines from the lift fan system when the engines are inthe turbofan mode. In some embodiments, a transmission may be disposedbetween the engines and the forced air bypass systems such that thetransmission engages the engines with the forced air bypass systems whenthe engines are in the turbofan mode and disengages the engines from theforced air bypass systems when the engines are in the turboshaft mode.

In certain embodiments, in the forward flight orientation, the forcedair bypass systems may be configured to generate a bypass ratio ofbetween 8 to 1 and 12 to 1. In some embodiments, an active flow controlsystem may be configured to generate control moments in the VTOLorientation and the forward flight orientation. In such embodiments, atleast a portion of the active flow control system may be integral withthe binary lift fan system and/or at least a portion of the active flowcontrol system may be integral with the exhaust systems. Also, in suchembodiments, the active flow control system may include pitch effectorsconfigured to generate pitch control moments in the forward flightorientation, roll effectors configured to generate roll control momentsin the forward flight orientation, roll effectors configured to generateroll control moments in the VTOL flight orientation, yaw effectorsconfigured to generate yaw control moments in the forward flightorientation and/or yaw effectors configured to generate yaw controlmoments in the VTOL flight orientation.

In another aspect, the present disclosure is directed to an aircraftoperable to transition between thrust-borne lift in a VTOL orientationand wing-borne lift in a forward flight orientation. The aircraftincludes a blended wing body having first and second engines disposedtherein. The engines have a turboshaft mode and a turbofan mode and areconfigured to generate engine exhaust. A binary lift fan system isdisposed within the body and includes ducted fans in a tandemlongitudinal orientation configured to generate pitch control moments inthe VTOL orientation. First and second forced air bypass systems aredisposed within the body and are configured to generate bypass air. Afirst exhaust system is coupled to the first engine and the first forcedair bypass system. A second exhaust system is coupled to the secondengine and the second forced air bypass system. An active flow controlsystem is configured to generate roll and yaw control moments in theVTOL orientation and pitch, roll and yaw control moments in the forwardflight orientation. In the VTOL orientation, the first and secondengines are in the turboshaft mode coupled to the lift fan system suchthat the first and second engines provide rotational energy to theducted fans generating the thrust-borne lift. In the forward flightorientation, the first and second engines are in the turbofan modecoupled to the first and second forced air bypass systems such that thebypass air combines with the engine exhaust in the respective first andsecond exhaust systems to provide forward thrust generating thewing-borne lift.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent disclosure, reference is now made to the detailed descriptionalong with the accompanying figures in which corresponding numerals inthe different figures refer to corresponding parts and in which:

FIGS. 1A-1H are schematic illustrations of a fan-in-wing blended wingbody aircraft and component parts thereof in accordance with embodimentsof the present disclosure;

FIGS. 2A-2S are schematic illustrations of ducted fans for a fan-in-wingblended wing body aircraft in accordance with embodiments of the presentdisclosure;

FIGS. 3A-3M are schematic illustrations of a pitch effector system andcomponent parts thereof for a fan-in-wing blended wing body aircraft inaccordance with embodiments of the present disclosure;

FIGS. 4A-4D are schematic illustrations of a roll effector system andcomponent parts thereof for a fan-in-wing blended wing body aircraft inaccordance with embodiments of the present disclosure;

FIGS. 5A-5K are schematic illustrations of a yaw effector system andcomponent parts thereof for a fan-in-wing blended wing body aircraft inaccordance with embodiments of the present disclosure;

FIGS. 6A-6F are schematic illustrations of a fan-in-wing blended wingbody aircraft in accordance with embodiments of the present disclosure;

FIGS. 7A-7I are schematic illustrations of a fan-in-wing blended wingbody aircraft and component parts thereof in accordance with embodimentsof the present disclosure;

FIGS. 8A-8F are schematic illustrations of a fan-in-wing blended wingbody aircraft in accordance with embodiments of the present disclosure;

FIGS. 9A-9I are schematic illustrations of a fan-in-wing blended wingbody aircraft and component parts thereof in accordance with embodimentsof the present disclosure; and

FIGS. 10A-10I are schematic illustrations of a fan-in-wing blended wingbody aircraft and component parts thereof in accordance with embodimentsof the present disclosure.

DETAILED DESCRIPTION

While the making and using of various embodiments of the presentdisclosure are discussed in detail below, it should be appreciated thatthe present disclosure provides many applicable inventive concepts,which can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed herein are merely illustrative and do notdelimit the scope of the present disclosure. In the interest of clarity,not all features of an actual implementation may be described in thepresent disclosure. It will of course be appreciated that in thedevelopment of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would be a routine undertakingfor those of ordinary skill in the art having the benefit of thisdisclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, and the like described herein may be positioned inany desired orientation. Thus, the use of terms such as “above,”“below,” “upper,” “lower” or other like terms to describe a spatialrelationship between various components or to describe the spatialorientation of aspects of such components should be understood todescribe a relative relationship between the components or a spatialorientation of aspects of such components, respectively, as the devicedescribed herein may be oriented in any desired direction. As usedherein, the term “coupled” may include direct or indirect coupling byany means, including moving and/or non-moving mechanical connections.

Referring to FIGS. 1A-1F in the drawings, various views of a fan-in-wingblended wing body aircraft 10 operable to transition betweenthrust-borne lift in a VTOL orientation and wing-borne lift in a forwardflight orientation are depicted. FIGS. 1A, 1C and 1E depict aircraft 10in the VTOL orientation wherein a lift fan system provides thrust-bornelift to the aircraft. FIGS. 1B, 1D and 1F depict aircraft 10 in theforward flight orientation wherein a forced air bypass system providesbypass air that combines with engine exhaust to generate forward thrustwith the forward airspeed of aircraft 10 providing wing-borne liftenabling aircraft 10 to have a high speed, high endurance, lowobservable forward flight mode. Aircraft 10 has a longitudinal axis 10 athat may also be referred to as the roll axis, a lateral axis 10 b thatmay also be referred to as the pitch axis and a vertical axis 10 c thatmay also be referred to as the yaw axis, as best seen in FIGS. 1A-1B.When longitudinal axis 10 a and lateral axis 10 b are both in ahorizontal plane, normal to the local vertical in the earth's referenceframe, aircraft 10 has a level flight attitude.

In the illustrated embodiment, aircraft 10 has an airframe 12 includinga fuselage 14 and a fixed wing 16 in the form of a blended wing body 18having an airfoil cross-section that generates lift responsive to theforward airspeed of aircraft 10. The outer skin of blended wing body 18may preferably be formed from high strength and lightweight materialssuch as carbon, metal, fiberglass, plastic or other suitable material orcombination of materials. In the illustrated embodiment, blended wingbody 18 has a rhombus shaped body with winglets 20 a, 20 b. As best seenin FIGS. 1A, 1C and 1E, aircraft 10 has a binary lift fan systemincluding lift fans 22 a, 22 b that are in a tandem lateral orientationsymmetrically disposed about longitudinal axis 10 a and symmetricallydisposed relative to the center of gravity of aircraft 10. In theillustrated embodiment, lift fans 22 a, 22 b are depicted as ducted fansin a fan-in-wing configuration.

During VTOL or hover operations when the lift fan system is providingthrust-borne lift for aircraft 10, butterfly doors 24 a, 24 b on theupper surface of blended wing body 18 and louvers 26 a, 26 b on thelower surface of blended wing body 18 are open to enable lift fans 22 a,22 b to generate airflow therethrough, thereby producing a verticalthrust. In other embodiments, louvers could be on the upper surface andbutterfly doors could be on the lower surface, louvers could be on theupper and lower surfaces or butterfly doors could be on the upper andlower surfaces. In the illustrated embodiment, louvers 26 a, 26 b arehinged parallel with the trailing edges of wing 16 such thatdifferential positioning of louvers 26 a, 26 b may be used to generateyaw control moments for aircraft 10 in VTOL flight mode and intransition flight modes, which are the flight modes during transitionsbetween VTOL flight mode and forward flight mode. In other embodiments,louvers 26 a, 26 b could have other orientations such as parallel withlongitudinal axis 10 a or lateral axis 10 b. In still other embodiments,the orientation of louvers 26 a, 26 b may be adjustable. Louvers 26 a,26 b may be electro-mechanically or hydraulically operated between theopen position of FIG. 1E and the closed position of FIG. 1F, whereinlouvers 26 a, 26 b form a portion of the lower airfoil surface ofaircraft 10. Likewise, butterfly doors 24 a, 24 b may beelectro-mechanically or hydraulically operated between the open positionof FIG. 1A and the closed position of FIG. 1B, wherein butterfly doors24 a, 24 b form a portion of the upper airfoil surface of aircraft 10.

Referring additionally to FIGS. 1G-1H, lift fans 22 a, 22 b includerotor assemblies 28 a, 28 b, respectively, each having a plurality ofvariable pitch rotor blades such that collective control of the rotorblades generates a variable thrust output at a constant rotor speed. Inother embodiments, the rotor assemblies could be fixed pitch, variablespeed rotor assemblies. Rotor assemblies 28 a, 28 b are coupled to aturboshaft engine 30 by suitable driveshafts and a transmission 32. Inother embodiments, rotor assemblies 28 a, 28 b could be driven byelectric motors. In the illustrated embodiment, engine 30 andtransmission 32 are disposed within blended wing body 18. Transmission32 preferably includes a clutching mechanism such that torque androtational energy may be selectively provided from engine 30 to rotorassemblies 28 a, 28 b. More particularly, when aircraft 10 is operatingin the VTOL mode, engine 30 is coupled to rotor assemblies 28 a, 28 b bytransmission 32 such that lift fans 22 a, 22 b generate thrust-bornelift for aircraft 10. When engine 30 is coupled to rotor assemblies 28a, 28 b, this will be referred to herein as the turboshaft configurationor turboshaft mode of engine 30. In addition, when aircraft 10 isoperating in the forward flight mode, engine 30 is decoupled to rotorassemblies 28 a, 28 b by the clutching mechanism of transmission 32 orother suitable clutching mechanism such that rotor assemblies 28 a, 28 bdo not rotate and are housed, respectively, between closed butterflydoors 24 a, 24 b and closed louvers 26 a, 26 b. In the transition modesof aircraft 10, engine 30 is preferably coupled to rotor assemblies 28a, 28 b by transmission 32 such that lift fans 22 a, 22 b generate atleast a portion of the lift for aircraft 10.

During forward flight, propulsive forward thrust is provided by a forcedair bypass system that is disposed within blended wing body 18. In theillustrated embodiment, the forced air bypass system includes inlets 34a, 34 b located proximate the nose of aircraft 10. The forced air bypasssystem also includes bypass fans 36 a, 36 b that are disposed withinblended wing body 18 downstream of inlets 34 a, 34 b, respectively.Bypass fans 36 a, 36 b provide air for engine 30 and also provide bypassair that travels around engine 30 via bypass ducts 38 a, 38 b that arecoupled to an exhaust system 40 of engine 30. In the illustratedembodiment, bypass fans 36 a, 36 b are coupled to engine 30 viatransmission 32 such that torque and rotational energy may beselectively provided from engine 30 to bypass fans 36 a, 36 b. It isnoted that transmission 32 may be housed in a single gearbox or multipleindependent gearboxes to provide suitable gear reduction from engine 30to lift fans 28 a, 28 b and bypass fans 36 a, 36 b, such that each canoperate at an optimum speed. When aircraft 10 is operating in theforward flight mode, engine 30 is coupled to bypass fans 36 a, 36 b bytransmission 32 such that bypass fans 36 a, 36 b generate bypass airthat combines with the engine exhaust in exhaust system 40 to provideforward thrust, thereby generating wing-borne lift responsive to theforward airspeed of aircraft 10. In addition, when aircraft 10 isoperating in the forward flight mode, engine 30 is decoupled to rotorassemblies 28 a, 28 b as discussed herein. When engine 30 is coupled tobypass fans 36 a, 36 b and decoupled from rotor assemblies 28 a, 28 b,this will be referred to herein as the turbofan configuration orturbofan mode of turboshaft engine 30, wherein shaft power extractedfrom engine 30 is used to power bypass fans 36 a, 36 b to generate thebypass air. When aircraft 10 is operating in the VTOL mode, engine 30may be decoupled from bypass fans 36 a, 36 b by the clutching mechanismof transmission 32 or other suitable clutching mechanism, such thatbypass fans 36 a, 36 b do not rotate. Alternatively, engine 30 mayremained coupled to bypass fans 36 a, 36 b in the VTOL mode such thatbypass fans 36 a, 36 b continue to rotate and provide cooling air formixing with engine exhaust. In the transition modes of aircraft 10,engine 30 is preferably coupled to bypass fans 36 a, 36 b such thatpropulsive thrust can generate forward airspeed and thus wing-bornelift.

In the illustrated embodiment, bypass fans 36 a, 36 b have a pressureratio of between 1.08 and 1.12. In other embodiments, the bypass fanscould have a pressure ratio either greater than 1.12 or less than 1.08.Also, in the illustrated embodiment, bypass fans 36 a, 36 b generate avery high bypass ratio (the mass flow rate of the bypass air to the massflow rate of air entering the engine) of between 8 to 1 and 12 to 1. Inother embodiments, the bypass fans could generate a bypass ratio eithergreater than 12 to 1 or less than 8 to 1. The bypass air generated bybypass fans 36 a, 36 b combines with the engine exhaust in exhaustsystem 40, which is configured with a thruster nozzle 42, to providepropulsive thrust. Thruster nozzle 42 may be a mixing nozzle in whichcase the bypass air mixes with the engine exhaust for a low-temperatureexhaust. Alternatively, thruster nozzle 42 may be a film cooled nozzlein which case the bypass air surrounds the engine exhaust forming aninsulating blanket along the internal surface of thruster nozzle 42keeping hot engine exhaust suitably remote from the components ofexhaust system 40.

Aircraft 10 is a fly-by-wire aircraft that operates responsive tocommand and control from a flight control system 44 that is preferably aredundant digital flight control system including multiple independentflight control computers. For example, the use of a redundant flightcontrol system 44 improves the overall safety and reliability ofaircraft 10 in the event of a failure in flight control system 44.Flight control system 44 may be implemented in a variety of formsincluding hardware, software, firmware, special purpose processors andcombinations thereof. Flight control system 44 preferably includesnon-transitory computer readable storage media including a set ofcomputer instructions executable by one or more processors forcontrolling the operation of aircraft 10. Flight control system 44 maybe implemented on one or more general-purpose computers, special purposecomputers or other machines with memory and processing capability. Forexample, flight control system 44 may include one or more memory storagemodules including, but is not limited to, internal storage memory suchas random access memory, non-volatile memory such as read only memory,removable memory such as magnetic storage memory, optical storage,solid-state storage memory or other suitable memory storage entity.Flight control system 44 may be a microprocessor-based system operableto execute program code in the form of machine-executable instructions.In addition, flight control system 44 may be selectively connectable toother computer systems via a proprietary encrypted network, a publicencrypted network, the Internet or other suitable communication networkthat may include both wired and wireless connections.

Flight control system 44 communicates via a wired communications networkwithin blended wing body 18 with various sensors, controllers andactuators associated with the systems of aircraft 10 such as lift fans22 a, 22 b, engine 30, transmission 32 and bypass fans 36 a, 36 b aswell as compressor 46, a pitch effector system including pitch effector48, a roll effector system including roll effectors 50 a, 50 b and a yaweffector system including yaw effectors 52 a, 52 b, as discussed herein.Flight control system 44 sends flight command information to the varioussystems to individually and independently control and operate eachsystem. For example, flight control system 44 is operable toindividually and independently control the thrust vectors generated bylift fans 22 a, 22 b, the pitch control moments generated by pitcheffector 48, the roll control moments generated by roll effectors 50 a,50 b and the yaw control moments generated by yaw effectors 52 a, 52 b.Flight control system 44 may autonomously control some or all aspects offlight operation for aircraft 10. Flight control system 44 maycommunicate with sensors, such as positioning sensors, attitude sensors,speed sensors, environmental sensors, fuel sensors, temperature sensors,location sensors and the like to enhance autonomous controlcapabilities. Flight control system 44 is also operable to communicatewith remote systems, such as a ground station via a wirelesscommunications protocol. The remote system may be operable to receiveflight data from and provide commands to flight control system 44 toenable remote flight control over some or all aspects of flightoperation for aircraft 10. As one example, flight control system 44 mayreceive a flight plan and/or mission parameters from a remote system andthereafter autonomously control all aspects of flight during themission.

Flight control system 44 may be configured to communicate with similarflight control systems in similar aircraft such that the flight controlsystems are networked together enabling cooperation and/or swarmbehavior. For example, such swarm behavior may include the ability todynamically adapt responsive to changing conditions or parametersincluding the ability for group coordination, distributed control,distributed tactical group planning, distributed tactical group goals,distributed strategic group goals and/or fully autonomous swarming. Moregenerally, aircraft 10 may be used in military, commercial, scientific,recreational and other applications. For example, military applicationsmay include intelligence, surveillance, reconnaissance and attackmissions. Civil applications include aerial photography, search andrescue missions, inspection of utility lines and pipelines, humanitarianaid including delivering food, medicine and other supplies toinaccessible regions, environment monitoring, border patrol missions,cargo transportation, forest fire detection and monitoring, accidentinvestigation and crowd monitoring, to name a few.

Flight control system 44 is the centralized host of all thefunctionality for the command and control of aircraft 10. Flight controlsystem 44 may execute any number of flight control modules and othermodules that may be implemented in a variety of forms includinghardware, software, firmware, special purpose processors andcombinations thereof. For example, flight control system 44 may executean active flow control module 54 that is configured to provide commandand control over selective mass flow injections that influence liftcoefficients, generate control moments and/or generate thrust vectorsfor aircraft 10 throughout the flight envelope that enable aircraft 10to have low observable characteristics compared to aircraft usingtraditional moving control surfaces such as open rotor disks, ailerons,elevators and rudders that can cause spikes in radar signature when theyare activated.

Referring additionally to FIG. 2A, a pressurized air system depicted asactive flow control system 56 will now be described. In the illustratedembodiment, active flow control system 56 is associated with and may beat least partially integral with the lift fan system. Active flowcontrol system 56 includes active flow control module 54 that isexecuted by flight control system 44. Active flow control system 56 alsoincludes engine 30 and a pressurized air source depicted as compressor46. In other embodiments, the pressurized air source could be bleed airfrom engine 30. In the illustrated embodiment, compressor 46 that ismechanically coupled to engine 30 such that shaft power extracted fromengine 30 is used to drive compressor 46 in all flight modes of aircraft10 including VTOL flight mode, forward flight mode and transition flightmodes. A lift fan manifold 58 is coupled to compressor 46 to distributepressurized air from compressor 46 to lift fan injectors 60 a associatedwith lift fan 22 a and lift fan injectors 60 b associated with lift fan22 b. The injection of pressurized air is controlled by a lift fan valvesystem 62 and a lift fan controller system 64 that includeselectro-mechanical actuators in communication with active flow controlmodule 54 that selectively open and close the valves within lift fanvalve system 62 for continuous and/or intermittent mass flow injections.

Referring additionally to FIGS. 2B-2Q, the operation of active flowcontrol system 56 in conjunction with the lift fan system will now bedescribed. FIG. 2B depicts a cross sectional view of lift fan 22 aduring VTOL operations of aircraft 10. It is noted that lift fan 22 a issubstantially similar to lift fan 22 b therefore, for sake ofefficiency, certain features have been disclosed only with regard tolift fan 22 a. One having ordinary skill in the art, however, will fullyappreciate an understanding of lift fan 22 b based upon the disclosureherein of lift fan 22 a. Lift fan 22 a is depicted as a ducted fanincluding a duct 70 having a generally annular inner surface 72, aninlet 74, an expanding diffuser 76 and an outlet 78. In the illustratedembodiment, expanding diffuser 76 has a diffuser angle between 10degrees and 20 degrees. In other embodiments, the diffuser angle of theduct of a lift fan could be less than 10 degrees or greater than 20degrees. A fan depicted as rotor assembly 28 a is disposed within duct70 between inlet 74 and expanding diffuser 76. Rotor assembly 28 a isconfigured to rotate relative to duct 70 about a fan axis 80 to generatean airflow therethrough depicted as inflow arrows 82 and outflow arrows84. In the illustrated embodiment, active flow control system 56includes a plurality of injection zones 86 a, 86 b, 86 c, 86 d that areuniformly and circumferentially distributed about inner surface 72 ofduct 70, as best seen in FIG. 2F, which also depicts lift fan 22 bhaving injection zones 88 a, 88 b, 88 c, 88 d.

Each of the injection zones 86 a, 86 b, 86 c, 86 d includes an injector60 a depicted as one or more slots in FIGS. 2B-2D and as a plurality ofjets in FIG. 2E. Similarly, each of the injection zones 88 a, 88 b, 88c, 88 d includes an injector 60 b as represented in FIG. 2A. Each of theinjectors 60 a is configured to inject a high speed mass flow in theform of pressurized air into duct 70 toward outlet 78, depicted asarrows 90 in FIGS. 2C-2E and as shading 92 in FIGS. 2G-2Q. In theillustrated embodiment, injectors 60 a are configured to injectpressurized air 90 tangential or substantially tangential to innersurface 72 of duct 70, as best seen in FIG. 2C. In other embodiments,injectors 60 a may be configured to inject pressurized air 90 tangentialor substantially tangential to expanding diffuser 76.

As depicted in FIGS. 2B and 2F, active flow control system 56 is notinjecting pressurized air into duct 70. As a result of the largediffuser angle of expanding diffuser 76, flow separation occurs betweenthe airflow and duct 70 along expanding diffuser 76, as indicated byseparated outflow arrow 84 a in FIG. 2B. In this configuration, lift fan22 a produces thrust having a thrust vector 94 a with a first magnitudeand with a direction that is substantially parallel to or substantiallycoincident with fan axis 80. As depicted in FIGS. 2C and 2G, active flowcontrol system 56 is injecting pressurized air into duct 70 from each ofthe injection zones 86 a, 86 b, 86 c, 86 d, as indicated by arrows 90 inFIG. 2C and shading 92 in FIG. 2G. As a result of the high speed massflow injection of pressurized air substantially tangential to innersurface 72 of duct 70, flow separation between the airflow and expandingdiffuser 76 is reduced and/or the airflow stays attached to expandingdiffuser 76 due to the coanda effect, as indicated by attached outflowarrow 84 b in FIG. 2C. In this configuration, lift fan 22 a producesthrust having a thrust vector 94 a with a second magnitude, which isgreater than the first magnitude due to the larger expansion ratio, andwith a direction that is substantially parallel to or substantiallycoincident with fan axis 80. During VTOL operations of aircraft 10, thestandard configuration of active flow control system 56 is preferablyinjecting pressurized air into duct 70 from each of the injection zones86 a, 86 b, 86 c, 86 d, as depicted in FIGS. 2C and 2G. In certainimplementations, however, the standard configuration of active flowcontrol system 56 during VTOL operations of aircraft 10 couldalternatively be not injecting pressurized air into duct 70, as depictedin FIGS. 2B and 2F.

In addition to being configurable to selectively inject pressurized airinto none or each of the injection zones 86 a, 86 b, 86 c, 86 d, activeflow control system 56 can be configured to selectively injectpressurized air into one or more specific injection zones 86 a, 86 b, 86c, 86 d to change the direction of thrust vector 94 a. Theseconfigurations of active flow control system 56 enable translation ofaircraft 10 during VTOL operations as well as the generation of yawcontrol moments during VTOL operations. These configurations of activeflow control system 56 can be achieved by activating the desiredinjection zone or zones from the configuration shown in FIGS. 2B and 2Fwherein no zones are active or by deactivating the required injectionzone or zones from the configuration shown in FIGS. 2C and 2G whereinall zones are active.

As depicted in FIGS. 2D-2E and 2H, active flow control system 56 isinjecting pressurized air into duct 70 in only the aft injection zone 86c, as indicated by arrows 90 in FIGS. 2D-2E and shading 92 in FIG. 2H.As a result of the high speed mass flow injection of pressurized airsubstantially tangential to inner surface 72 in injection zone 86 c,flow separation between the airflow and expanding diffuser 76 downstreamof injection zone 86 c is reduced and/or the airflow stays attached toexpanding diffuser 76 downstream of injection zone 86 c, as indicated byattached outflow arrow 84 b in FIGS. 2D-2E. At the same time, as nopressurized air is injected in injection zones 86 a, 86 b, 86 d, flowseparation occurs between the airflow and expanding diffuser 76downstream of injection zones 86 a, 86 b, 86 d as indicated by separatedoutflow arrow 84 a in FIGS. 2D-2E. The selective injection ofpressurized air into specific ones of injection zones 86 a, 86 b, 86 c,86 d asymmetrically reduces the flow separation between the airflow andexpanding diffuser 76 downstream of the injection zones in whichinjection is occurring. In this case, when only the aft injection zone86 c is operating, the airflow through lift fan 22 a is influenced ordeflected toward expanding diffuser 76 downstream of aft injection zone86 c. This changes the direction of thrust vector 94 a such that thrustvector 94 a has a non-zero angle relative to the direction of fan axis80, such as an angle between 5 degrees and 10 degrees in the directionopposite aft injection zone 86 c, in this case the forward direction, asindicated by the tilt of thrust vector 94 a in FIGS. 2D-2E and thepresentation of the forward component of thrust vector 94 a in FIG. 2H.When only the aft injection zones 86 c, 88 c are active, as shown inFIG. 2H, thrust vectors 94 a, 94 b have forward components that urgeaircraft 10 to translate in the forward direction during VTOLoperations.

Similarly, when only the forward injection zones 86 a, 88 a are active,as shown in FIG. 2I, thrust vectors 94 a, 94 b have aft components thaturge aircraft 10 to translate in the aft direction during VTOLoperations. FIG. 2J illustrates active flow control system 56 injectingpressurized air into only the left injection zones 86 d, 88 d such thatthrust vectors 94 a, 94 b have right components that urge aircraft 10 totranslate to the right during VTOL operations. FIG. 2K illustratesactive flow control system 56 injecting pressurized air into only theright injection zones 86 b, 88 b such that thrust vectors 94 a, 94 bhave left components that urge aircraft 10 to translate to the leftduring VTOL operations. Active flow control system 56 is operable toinject the pressurized air at a variable intensity such that the rate oftranslation of aircraft 10 can be controlled by changing the intensitylevel or mass flowrate of the pressurized air.

In addition to providing translation authority to aircraft 10 duringVTOL or hover operations, active flow control system 56 can beconfigured to provide yaw authority to aircraft 10 during VTOL or hoveroperations. FIG. 2L illustrates active flow control system 56 injectingpressurized air into forward injection zone 86 a of lift fan 22 a andinto aft injection zone 88 c of lift fan 22 b. The selective injectionof pressurized air into forward injection zone 86 a asymmetricallyreduces the flow separation between the airflow and expanding diffuser76 downstream of forward injection zone 86 a generating a thrust vector94 a having an aft component. The selective injection of pressurized airinto aft injection zone 88 c asymmetrically reduces the flow separationbetween the airflow and the expanding diffuser downstream of aftinjection zone 88 c generating a thrust vector 94 b having a forwardcomponent. The aft component of thrust vector 94 a and the forwardcomponent of thrust vector 94 b create yaw control moments about thecenter of gravity of aircraft 10 such that aircraft 10 is urged torotate right about vertical axis 10 c. Similarly, FIG. 2M illustratesactive flow control system 56 injecting pressurized air into aftinjection zone 86 c of lift fan 22 a and into forward injection zone 88a of lift fan 22 b. This operation causes thrust vector 94 a to have aforward component and thrust vector 94 b to have an aft component whichcreate yaw control moments about the center of gravity of aircraft 10such that aircraft 10 is urged to rotate left about vertical axis 10 c.Active flow control system 56 is operable to inject the pressurized airat a variable intensity such that the rate of the yaw maneuver ofaircraft 10 can be controlled by changing the intensity level or massflowrate of the pressurized air.

While the benefits of activating a single injection zone of a fourinjection zones active flow control system for lift fans has beendescribed and depicted, it should be understood by those having ordinaryskill in the art that activating other combinations or permutations ofinjection zones in a four injection zones active flow control system forlift fans is also beneficial. For example, FIG. 2N depicts activation ofinjection zones 86 b, 86 c of lift fan 22 a and injection zones 88 b, 88c of lift fan 22 b. This operation causes thrust vector 94 a to have aforward and left component and causes thrust vector 94 b to have aforward and left component which urge aircraft 10 to translatediagonally in the forward/left direction. Similarly, FIG. 2O depictsactivation of injection zones 86 c, 86 d of lift fan 22 a and injectionzones 88 c, 88 d of lift fan 22 b. This operation causes thrust vector94 a to have a forward and right component and causes thrust vector 94 bto have a forward and right component which urge aircraft 10 totranslate diagonally in the forward/right direction.

Even though the active flow control system 56 associated with the liftfan system has been described and depicted as including four injectionzones for each lift fan, it should be understood by those havingordinary skill in the art that lift fan systems can have other numbersof active flow control injection zones both less than or greater thanfour. For example, FIG. 2P depicts an embodiment of lift fans 22 a, 22 bin which lift fan 22 a has two active flow control injection zones 86 e,86 f and lift fan 22 b has two active flow control injection zones 88 e,88 f that enable fore/aft translation in hover as well as yaw controlauthority in hover. Similarly, FIG. 2Q depicts an embodiment of liftfans 22 a, 22 b in which lift fan 22 a has eight active flow controlinjection zones 86 g-86 n and lift fan 22 b has eight active flowcontrol injection zones 88 g-88 n that enable fore/aft translation,left/right translation and diagonal translation in hover as well as yawcontrol authority in hover.

FIGS. 2R-2S depict cross sectional views of wing 16 along a chord thatpasses through lift fan 22 a during transition flight of aircraft 10when lift fan 22 a experiences edgewise flow. In the illustratedembodiment, duct 70 of lift fan 22 a has a generally annular innersurface 72, an inlet 74 with a leading portion 74 a, an expandingdiffuser 76 with a trailing portion 76 a and an outlet 78. Rotorassembly 28 a is disposed within duct 70 between inlet 74 and expandingdiffuser 76 and is configured to rotate relative to duct 70 about a fanaxis 80 to generate an airflow therethrough depicted as streamlines 96a, 96 b, 96 c, 96 d. In addition, streamline 96 e is depicted astraveling above wing 16 and streamline 96 f is depicted as travelingbelow wing 16. In the illustrated embodiment, active flow control system56 utilizes an upper forward injection zone 86 e and aft injection zone86 c, each of which includes an injector 60 a in the form of one or moreslots or a plurality of jets, as discussed herein. Injector 60 a in aftinjection zone 86 c is configured to inject a high speed mass flow inthe form of pressurized air into duct 70 tangential or substantiallytangential to inner surface 72 of duct 70 toward outlet 78, depicted asarrows 90 in FIG. 2S. Injector 60 a in forward injection zone 86 e isconfigured to inject a high speed mass flow in the form of pressurizedair tangential or substantially tangential to an upper surface ofleading portion 74 a of duct 70 toward inlet 74, depicted as arrows 98in FIG. 2S.

Depending upon factors such as the forward airspeed of aircraft 10 thatis generating the edgewise flow relative to lift fan 22 a, forwardinjection zone 86 e and aft injection zone 86 c may have circumferentialspans up to ninety degrees, between sixty degrees and ninety degrees, upto sixty degrees, between thirty degrees and sixty degrees or othersuitable circumferential spans. It is noted that the circumferentialspan of forward injection zone 86 e may be the same as or different fromthe circumferential span of aft injection zone 86 c. For example, thecircumferential span of forward injection zone 86 e may have a ratio tothe circumferential span of aft injection zone 86 c of 4 to 1; 3 to 1; 2to 1; 1 to 1; 1 to 2; 1 to 3; 1 to 4 or other suitable ratio. In oneexample, the circumferential span of forward injection zone 86 e may bebetween sixty degrees and ninety degrees while the circumferential spanof aft injection zone 86 c may be between thirty degrees and sixtydegrees.

As depicted in FIG. 2R, active flow control system 56 is not injectingpressurized air into duct 70. As a result, flow separation occursbetween the airflow and duct 70 along inner surface 72 downstream ofleading portion 74 a as indicated by the gap between inner surface 72and streamline 96 a. Also illustrated is turbulent and/or recirculatoryair 96 g at the flow separation region that causes noise pollution andreduces the efficiency of lift fan 22 a. Similarly, flow separationoccurs between the airflow and duct 70 along expanding diffuser 76 attrailing portion 76 a as indicated by the gap between expanding diffuser76 and streamline 96 d, which further reduces the efficiency of lift fan22 a.

As depicted in FIG. 2S, active flow control system 56 is injectingpressurized air into duct 70 in forward injection zone 86 e and aftinjection zone 86 c, as indicated by arrows 98, 90, in FIG. 2S. As aresult of the high speed mass flow injection of pressurized airsubstantially tangential to the upper surface of leading portion 74 a ofduct 70 toward inlet 74, flow separation between the airflow and duct 70along inner surface 72 downstream of leading portion 74 a is reducedand/or the airflow stays attached to inner surface 72 due to the coandaeffect, as indicated by the reduction in the gap between inner surface72 and streamline 96 a as well as the absence of recirculatory air 96 gin FIG. 2S. Similarly, as a result of the high speed mass flow injectionof pressurized air substantially tangential to inner surface 72 of duct70 toward outlet 78, flow separation between the airflow and duct 70along expanding diffuser 76 at trailing portion 76 a is reduced and/orthe airflow stays attached to expanding diffuser 76 due to the coandaeffect, as indicated by the reduction in the gap between expandingdiffuser 76 and streamline 96 d in FIG. 2S. Use of active flow controlsystem 56 in this manner not only improves the forward flightcharacteristics of the lift fan system in edgewise flight by increasingthrust efficiency and allowing for smoother transition betweenthrust-borne lift and wing-borne flight, but also reduces powerconsumption and loads on the rotor systems.

Referring now to FIGS. 1B, 1H and 3A, a portion of the active flowcontrol system that will be referred to herein as pitch effector system100 will now be described. As best seen in FIG. 1B, pitch effector 48 isdisposed proximate the trailing edge of wing 16 aft of fuselage 14.Pitch effector 48 is associated with and may be at least partiallyintegral with the exhaust system of aircraft 10. While pitch effector 48is most effective when aircraft 10 is operating in forward flight modewhen the exhaust system is discharging a propulsive gas stream, pitcheffector 48 may also be used when aircraft 10 is operating in VTOLflight mode and transition flight modes when the exhaust system may bedischarging a non-propulsive gas stream. In the embodiment illustratedin FIG. 3A, pitch effector system 100 includes active flow controlmodule 54 that is executed by flight control system 44. Pitch effectorsystem 100 also includes engine 30 and compressor 46. A pitch manifold102 is coupled to compressor 46 to distribute pressurized air fromcompressor 46 to upper pitch injector 104 and lower pitch injector 106of pitch effector 48 which is associated with exhaust system 40 ofaircraft 10 and more specifically with thruster nozzle 42. The injectionof pressurized air is controlled by a pitch valve system 108 and a pitchcontroller system 110 that includes electro-mechanical actuators incommunication with active flow control module 54 that selectively openand close the valves within pitch valve system 108 for continuous and/orintermittent mass flow injections.

Referring additionally to FIGS. 3B-3D, pitch effector 48 and thrusternozzle 42 of aircraft 10 are shown in greater detail. In the illustratedembodiment, thruster nozzle 42 may be referred to as a flat nozzle andis depicted as a diverging nozzle having an upper expansion ramp 112 anda lower expansion ramp 114 that enable thruster nozzle 42 to discharge apropulsive gas; namely, bypass air combined with engine exhaust, in anaftward direction to generate forward thrust for aircraft 10. FIG. 3Cdepicts an upper surface 116 of thruster nozzle 42 having upper pitchinjector 104 of pitch effector 48 coupled thereto. In the illustratedembodiment, upper pitch injector 104 is depicted as a plurality of jets118 distributed proximate the aft end of thruster nozzle 42. FIG. 3Ddepicts a lower surface 120 of thruster nozzle 42 having lower pitchinjector 106 of pitch effector 48 coupled thereto. In the illustratedembodiment, lower pitch injector 106 is depicted as two slots 122proximate the aft end of thruster nozzle 42. Even though upper pitchinjector 104 is depicted as a plurality of jets and lower pitch injector106 is depicted as a pair of slots, it should be understood by thosehave ordinary skill in the art that both upper pitch injector 104 andlower pitch injector 106 could be a plurality of jets, both upper pitchinjector 104 and lower pitch injector 106 could be one or more slots orupper pitch injector 104 could be one or more slots and lower pitchinjector 106 could be a plurality of jets.

Referring additionally to FIGS. 3E-3G, the operation of pitch effector48 will now be described. FIGS. 3E-3G are schematic cross sectionalviews of the aft end of thruster nozzle 42 showing upper pitch injector104, lower pitch injector 106, upper expansion ramp 112 and lowerexpansion ramp 114. In FIG. 3F, pitch effector 48 is not injectingpressurized air into thruster nozzle 42. As a result, propulsive gas 124is directed aftward from thruster nozzle 42 having a forward thrustvector that is substantially parallel to longitudinal axis 10 a. In thisconfiguration, pitch effector 48 is not generating a pitch controlmoment. In FIG. 3E, pitch effector 48 is injecting pressurized air intothruster nozzle 42 from lower pitch injector 106 transverse to orsubstantially normal to the flow of propulsive gas 124, as indicated byarrow 126. As a result of the high speed mass flow injection ofpressurized air, the stream of propulsive gas 124 is deflected ordiverted toward upper expansion ramp 112 such that propulsive gas 124exits thruster nozzle 42 having an aftward and upward direction whichgenerates a thrust vector having a downward component, as indicated byarrow 128, which is aft of the center of gravity of aircraft 10, therebygenerating a pitch up control moment.

In FIG. 3G, pitch effector 48 is injecting pressurized air into thrusternozzle 42 from upper pitch injector 104 transverse to or substantiallynormal to the flow of propulsive gas 124, as indicated by arrow 130. Asa result of the high speed mass flow injection of pressurized air, thestream of propulsive gas 124 is deflected or diverted toward lowerexpansion ramp 114 such that propulsive gas 124 exits thruster nozzle 42having an aftward and downward direction which generates a thrust vectorhaving an upward component, as indicated by arrow 132, which is aft ofthe center of gravity of aircraft 10, thereby generating a pitch downcontrol moment. In this manner, pitch effector 48 acts as a fluidicthrust vectoring system that selectively directs the stream ofpropulsive gas 124 upward or downward as propulsive gas 124 exitsthruster nozzle 42 to generate pitch control moments. It is noted thatpitch effector 48 is operable to inject the pressurized air at avariable intensity such that the rate of pitch maneuvers of aircraft 10can be controlled by changing the intensity level or mass flowrate ofthe pressurized air.

Referring now to FIGS. 3H-3J, another embodiment of pitch effector 48will now be described. FIGS. 3H-3J are schematic cross sectional viewsof the aft end of a thruster nozzle 140 having a lower pitch injector142 and a lower expansion ramp 144. In FIG. 3J, pitch effector 48 is notinjecting pressurized air into thruster nozzle 140. As a result,propulsive gas 124 tends to attach to lower expansion ramp 144 such thatpropulsive gas 124 exits thruster nozzle 140 having an aftward anddownward direction that generates a thrust vector having an upwardcomponent, as indicated by arrow 146, which is aft of the center ofgravity of aircraft 10, thereby generating a pitch down control moment.In FIG. 3I, pitch effector 48 is injecting pressurized air into thrusternozzle 140 from lower pitch injector 142 transverse to or substantiallynormal to the flow of propulsive gas 124 at a first intensity, asindicated by small arrow 148. As a result of the high speed mass flowinjection of pressurized air, the stream of propulsive gas 124 isdeflected or diverted away from lower expansion ramp 144 such thatpropulsive gas 124 exits thruster nozzle 140 directed aftward fromthruster nozzle 140 having a forward thrust vector that is substantiallyparallel to longitudinal axis 10 a. In this configuration, pitcheffector 48 is not generating a pitch control moment. In FIG. 3H, pitcheffector 48 is injecting pressurized air into thruster nozzle 140 fromlower pitch injector 142 transverse to or substantially normal to theflow of propulsive gas 124 at a second intensity that is greater thanthe first intensity, as indicated by large arrow 150. As a result of thehigh speed mass flow injection of pressurized air, the stream ofpropulsive gas 124 is deflected or diverted farther away from lowerexpansion ramp 114 such that propulsive gas 124 exits thruster nozzle140 having an aftward and upward direction that generates a thrustvector having a downward component, as indicated by arrow 152, which isaft of the center of gravity of aircraft 10, thereby generating a pitchup control moment. In this manner, pitch effector 48 acts as a fluidicthrust vectoring system that selectively directs the stream ofpropulsive gas 124 upward as propulsive gas 124 exits thruster nozzle140 to generate pitch control moments. It is noted that when pitcheffector 48 is used with thruster nozzle 140, pitch effector 48 defaultsto the configuration shown in FIG. 3I such that no pitch control momentis being generated.

Referring now to FIGS. 3K-3M, the operation a further embodiment ofpitch effector 48 will now be described. FIGS. 3K-3M are schematic crosssectional views of the aft end of thruster nozzle 160 having a diverter162 disposed therein that includes an upper pitch injector 164, a lowerpitch injector 166, an upper surface 168, a lower surface 170 and coandasurface 172. In FIG. 3L, pitch effector 48 is not injecting pressurizedair. As a result, propulsive gas 124 is directed around diverter 162 andaftward from thruster nozzle 160 having a forward thrust vector that issubstantially parallel to longitudinal axis 10 a. In this configuration,pitch effector 48 is not generating a pitch control moment. In FIG. 3K,pitch effector 48 is injecting pressurized air into thruster nozzle 160from lower pitch injector 166 substantially tangential to lower surface170, as indicated by arrow 174. As a result of the high speed mass flowinjection of pressurized air, the stream of propulsive gas 124 tends toattach to coanda surface 172 such that propulsive gas 124 exits thrusternozzle 160 having an aftward and upward direction that generates athrust vector having a downward component, as indicated by arrow 176,which is aft of the center of gravity of aircraft 10, thereby generatinga pitch up control moment. In FIG. 3M, pitch effector 48 is injectingpressurized air into thruster nozzle 160 from upper pitch injector 164substantially tangential to upper surface 168, as indicated by arrow178. As a result of the high speed mass flow injection of pressurizedair, the stream of propulsive gas 124 tends to attach to coanda surface172 such that propulsive gas 124 exits thruster nozzle 160 having anaftward and downward direction that generates a thrust vector having anupward component, as indicated by arrow 180, which is aft of the centerof gravity of aircraft 10, thereby generating a pitch down controlmoment. In this manner, pitch effector 48 acts as a fluidic thrustvectoring system that selectively influences the stream of propulsivegas 124 to turn upward or downward as propulsive gas 124 exits thrusternozzle 160 to generate pitch control moments. It is noted that pitcheffector 48 is operable to inject the pressurized air at a variableintensity such that the rate of pitch maneuvers of aircraft 10 can becontrolled by changing the intensity level or mass flowrate of thepressurized air.

Referring now to FIGS. 1B, 1H and 4A, a portion of the active flowcontrol system that will be referred to herein as roll effector system200 will now be described. As best seen in FIG. 1B, roll effectors 50 a,50 b are disposed proximate the trailing edge of wing 16 inboard ofwinglets 20 a, 20 b, respectively. While roll effectors 50 a, 50 b aremost effective when aircraft 10 is operating in forward flight mode,roll effectors 50 a, 50 b may also be used when aircraft 10 is operatingin VTOL flight mode and transition flight modes. It is noted that whenaircraft 10 is operating in VTOL flight mode and transition flightmodes, differential thrust generated by lift fans 22 a, 22 b may be usedto effectively provide roll control authority. In the embodimentillustrated in FIG. 4A, roll effector system 200 includes active flowcontrol module 54 that is executed by flight control system 44. Rolleffector system 200 also includes engine 30 and compressor 46. A rollmanifold 202 is coupled to compressor 46 to distribute pressurized airfrom compressor 46 to upper right injector 204 and lower right injector206 of roll effector 50 b and upper left injector 208 and lower leftinjector 210 of roll effector 50 a. As discussed herein, each ofinjectors 204, 206, 208, 210 may be formed from one or more slots or maybe formed from a plurality of jets. The injection of pressurized air iscontrolled by a roll valve system 212 and a roll controller system 214that includes electro-mechanical actuators in communication with activeflow control module 54 that selectively open and close valves withinroll valve system 212 for continuous and/or intermittent mass flowinjections.

Referring now to FIGS. 4B-4D, the operation of roll effector 50 a willnow be described. It is noted that roll effector 50 a is substantiallysimilar to roll effector 50 b therefore, for sake of efficiency, certainfeatures have been disclosed only with regard to roll effector 50 a. Onehaving ordinary skill in the art, however, will fully appreciate anunderstanding of roll effector 50 b based upon the disclosure herein ofroll effector 50 a. FIGS. 4B-4D are schematic cross sectional views ofwing 16 of aircraft 10 along a chord that passes through roll effector50 a. In the illustrated embodiment, roll effector 50 a forms a lateralslot in the trailing edge of wing 16 having a generally laterallyextending diverter 216 positioned therein. Diverter 216 is disposedbetween upper left injector 208 and lower left injector 210. Diverter216 has an upper surface 218, a lower surface 220 and coanda surface222. In FIG. 4C, roll effector 50 a is not injecting pressurized air. Asa result, airflow across wing 16, as depicted by streamlines 224, 226,is uninfluenced by roll effector 50 a such that roll effector 50 a isnot generating a roll control moment. In FIG. 4B, roll effector 50 a isinjecting pressurized air from upper left injector 208 substantiallytangential to upper surface 218, as indicated by arrow 228. As a resultof the high speed mass flow injection of pressurized air, airflow acrosswing 16 is diverted downwardly due to the coanda effect, as indicated bythe trailing ends of streamlines 230, 232, which increases the liftgenerated by wing 16 proximate roll effector 50 a, thereby generating aroll right control moment for aircraft 10.

In FIG. 4D, roll effector 50 a is injecting pressurized air from lowerleft injector 210 substantially tangential to lower surface 220, asindicated by arrow 234. As a result of the high speed mass flowinjection of pressurized air, airflow across wing 16 is divertedupwardly due to the coanda effect, as indicated by the trailing ends ofstreamlines 236, 238, which decreases the lift generated by wing 16proximate roll effector 50 a, thereby generating a roll left controlmoment. Preferably, roll effectors 50 a, 50 b are operateddifferentially such that when it is desired to generate a roll leftcontrol moment, roll effector 50 a injects pressurized air from lowerleft injector 210 and roll effector 50 b injects pressurized air fromupper right injector 204 to generate symmetric roll left controlmoments. Likewise, when it is desired to generate a roll right controlmoment, roll effector 50 a injects pressurized air from upper leftinjector 208 and roll effector 50 b injects pressurized air from lowerright injector 206 to generate symmetric roll right control moments. Inthis manner, roll effectors 50 a, 50 b selectively direct the airflowacross wing 16 upward or downward to generate roll control moments. Itis noted that roll effectors 50 a, 50 b are operable to inject thepressurized air at a variable intensity such that the rate of rollmaneuvers of aircraft 10 can be controlled by changing the intensitylevel or mass flowrate of the pressurized air.

Referring now to FIGS. 1B, 1H and 5A, a portion of the active flowcontrol system that will be referred to herein as yaw effector system300 will now be described. As best seen in FIG. 1B, yaw effectors 52 a,52 b are disposed proximate the trailing edge of winglets 20 a, 20 b,respectively. While yaw effectors 52 a, 52 b are most effective whenaircraft 10 is operating in forward flight mode; yaw effectors 52 a, 52b also have functionality in VTOL flight mode and transition flightmodes, as discussed herein. It is noted that when aircraft 10 isoperating in VTOL flight mode and transition flight modes, the activeflow control system associated with lift fans 22 a, 22 b may be used toeffectively provide yaw control authority. In the embodiment illustratedin FIG. 5A, yaw effector system 300 includes active flow control module54 that is executed by flight control system 44. Yaw effector system 300also includes engine 30 and compressor 46. A yaw manifold 302 is coupledto compressor 46 to distribute pressurized air from compressor 46 toupper right injector 304 and lower right injector 306 of yaw effector 52b and upper left injector 308 and lower left injector 310 of yaweffector 52 a. As discussed herein, each of injectors 304, 306, 308, 310may be in the form of one or more slots or a plurality of jets. Forexample, FIG. 5B is a top view of an embodiment of yaw effector 52 awherein upper left injector 308 is depicted as a single slot. As anotherexample, FIG. 5C is a top view of another embodiment of yaw effector 52a wherein upper left injector 308 is depicted as a plurality of jets.The injection of pressurized air by yaw effector system 300 iscontrolled by a yaw valve system 312 and a yaw controller system 314that includes electro-mechanical actuators in communication with activeflow control module 54 that selectively open and close valves within yawvalve system 312 for continuous and/or intermittent mass flowinjections.

Referring now to FIGS. 5D-5F, the operation a yaw effector 52 a will nowbe described. It is noted that yaw effector 52 a is substantiallysimilar to yaw effector 52 b therefore, for sake of efficiency, certainfeatures have been disclosed only with regard to yaw effector 52 a. Onehaving ordinary skill in the art, however, will fully appreciate anunderstanding of yaw effector 52 b based upon the disclosure herein ofyaw effector 52 a. FIGS. 5D-5F are schematic cross sectional views ofwing 16 of aircraft 10 along a chord that passes through yaw effector 52a. In the illustrated embodiment, yaw effector 52 a includes upper leftinjector 308 and lower left injector 310. In FIG. 5D, yaw effector 52 ais not injecting pressurized air from upper left injector 308 or lowerleft injector 310 such that the airflow across wing 16 is uninfluencedby yaw effector 52 a, as indicated by streamlines 316, 318 passing overand under wing 16. In this configuration, yaw effector 52 a is notgenerating a yaw control moment. In FIG. 5E, yaw effector 52 a isinjecting pressurized air from upper left injector 308 and lower leftinjector 310 transverse to or substantially normal to the airflow acrosswing 16 at a first intensity, as indicated by small arrows 320, 322. Asa result of the high speed mass flow injection of pressurized air, theairflow above wing 16 proximate yaw effector 52 a is deflected ordiverted upward, as indicated by the trailing end of streamline 324 andthe airflow below wing 16 proximate yaw effector 52 a is deflected ordiverted downward, as indicated by the trailing end of streamline 326.In this configuration, yaw effector 52 a is disrupting the airflowacross wing 16 proximate yaw effector 52 a creating a drag rudder in theform of a fluidic split flap, thereby generating a yaw left controlmoment.

It is noted that yaw effectors 52 a, 52 b are operable to inject thepressurized air at a variable intensity such that the rate of yawmaneuvers of aircraft 10 can be controlled by changing the intensitylevel or mass flowrate of the pressurized air. For example, asillustrated in FIG. 5F, yaw effector 52 a is injecting pressurized airfrom upper left injector 308 and lower left injector 310 transverse toor substantially normal to the airflow across wing 16 at a secondintensity that is greater than the first intensity, as indicated bylarge arrows 328, 330. As a result of the high speed mass flow injectionof pressurized air, the airflow above wing 16 proximate yaw effector 52a is deflected or diverted upward, as indicated by the trailing end ofstreamline 332 and the airflow below wing 16 proximate yaw effector 52 ais deflected or diverted downward, as indicated by the trailing end ofstreamline 334. In this configuration, yaw effector 52 a creates alarger disruption in the airflow across wing 16 proximate yaw effector52 a creating a larger drag rudder and thus a larger yaw left controlmoment.

For effective yaw authority, the operation of yaw effectors 52 a, 52 bis coordinated such that when a yaw left control moment is desired, leftyaw effector 52 a injects pressurized air while right yaw effector 52 bdoes not inject pressurized air or left yaw effector 52 a injectspressurized air at a greater intensity than right yaw effector 52 b.Similarly, when a yaw right control moment is desired, right yaweffector 52 b injects pressurized air while left yaw effector 52 a doesnot inject pressurized air or right yaw effector 52 b injectspressurized air at a greater intensity than left yaw effector 52 a. Inthis manner, yaw effectors 52 a, 52 b selectively direct the airflowacross wing 16 upward and downward to generate yaw control moments.

In addition to generating yaw control moments during forward flight, yaweffectors 52 a, 52 b are also configurable to generate roll controlmoments in hover. For example, to generate roll right control moments,yaw effector 52 a injects pressurized air from lower left injector 310while at the same time, yaw effector 52 b injects pressurized air fromupper right injector 304. As a result of the high speed mass flow ofpressurized air injected from yaw effectors 52 a, 52 b, aircraft 10 isurged to rotate about longitudinal axis 10 a in a roll right maneuverduring hover. Similarly, to generate roll left control moments, yaweffector 52 a injects pressurized air from upper left injector 308 whileat the same time, yaw effector 52 b injects pressurized air from lowerright injector 306. As a result of the high speed mass flow ofpressurized air injected from yaw effectors 52 a, 52 b, aircraft 10 isurged to rotate about longitudinal axis 10 a in a roll left maneuverduring hover. In this manner, differential operation of yaw effectors 52a, 52 can be used to generate roll control moments in hover. During thisoperation, yaw effectors 52 a, 52 could also be referred to as rolleffectors 52 a, 52 b. It is noted that roll effectors 52 a, 52 b areoperable to inject the pressurized air at a variable intensity such thatthe rate of roll maneuvers of aircraft 10 can be controlled by changingthe intensity level or mass flowrate of the pressurized air.

Referring now to FIGS. 5G-5K, another embodiment of a yaw effector 340will now be described. It is noted that one yaw effector 340 wouldpreferably be used as the left yaw effector while another yaw effector340 is being used as the right yaw effector. Yaw effector 340 includesan upper injector 342 and lower injector 344 that are depicted as slotsin FIG. 5G and as a plurality of jets in FIG. 5H. Yaw effector 340 alsoincludes an upper flow disrupter 346, a lower flow disrupter 348 and anaftwardly extending airfoil extension 350, as best seen in FIGS. 5I-5K.In the illustrated embodiment, upper flow disrupter 346 and lower flowdisrupter 348 are discontinuities or step changes in the airfoil surfaceof wing 16 which cause airflow across wing 16 at yaw effector 340 toseparate from the wing surface and/or become turbulent. In FIG. 5K, yaweffector 340 is not injecting pressurized air from upper injector 342 orlower injector 344. As a result, airflow across wing 16 is influenced byupper flow disrupter 346 and lower flow disrupter 348, as indicated bythe separation and/or turbulence at the trailing ends of streamlines352, 354 passing over and under wing 16. This flow separation and/orturbulence creates a drag rudder proximate yaw effector 340 generating ayaw control moment.

In FIG. 5J, yaw effector 340 is injecting pressurized air from upperinjector 342 and lower injector 344 tangential or substantiallytangential to airfoil extension 350 at a first intensity, as indicatedby small arrows 356, 358. As a result of the high speed mass flowinjection of pressurized air, the flow separation and/or turbulence ofthe airflow above and below wing 16 proximate yaw effector 52 a issignificantly reduced, as indicated by the trailing end of streamlines360, 362 passing over and under wing 16. The reduction in flowseparation and/or turbulence lowers the drag proximate yaw effector 340such that yaw effector 340 forms a fluidic airfoil extension. Thisconfiguration is preferably the default configuration of yaw effector340 during forward flight in which yaw effector 340 is not generating ayaw control moment. In FIG. 5I, yaw effector 340 is injectingpressurized air from upper injector 342 and lower injector 344tangential or substantially tangential to airfoil extension 350 at asecond intensity that is greater than the first intensity, as indicatedby large arrows 364, 366. As a result of the high speed mass flowinjection of pressurized air, the flow separation and/or turbulence ofthe airflow above and below wing 16 proximate yaw effector 52 a is notonly eliminated, as indicated by the trailing end of streamlines 366,368 passing over and under wing 16, but the mass flow of the pressurizedair generates substantial forward thrust. This added forward thrustcreated by yaw effector 340 generates a yaw control moment.

For effective yaw authority, the operation of a left yaw effector 340and a right yaw effector 340 are coordinated such that when a yaw leftcontrol moment is desired, left yaw effector 340 transitions frominjecting pressurized air at the first intensity (FIG. 5J) to notinjecting pressurized air (FIG. 5K) and/or right yaw effector 340transitions from injecting pressurized air at the first intensity (FIG.5J) to injecting pressurized air at the second intensity (FIG. 5I).Similarly, when a yaw right control moment is desired, left yaw effector340 transitions from injecting pressurized air at the first intensity(FIG. 5J) to injecting pressurized air at the second intensity (FIG. 5I)and/or right yaw effector 340 transitions from injecting pressurized airat the first intensity (FIG. 5J) to not injecting pressurized air (FIG.5K). In this manner, an aircraft with using yaw effectors 340selectively adjusts the amount of drag created as the airflow acrosswing 16 passes over and under yaw effectors 340 to generate yaw controlmoments.

In addition to generating yaw control moments during forward flight, yaweffectors 340 are also configurable to generate yaw control moments inhover. For example, when a yaw right control moment is desired, left yaweffector 340 would inject pressurized air aftwardly from upper injector342 and lower injector 344 at the second intensity while right yaweffector 340 would not inject pressurized air. Similarly, when a yawleft control moment is desired, right yaw effector 340 would injectpressurized air aftwardly from upper injector 342 and lower injector 344at the second intensity while left yaw effector 340 would not injectpressurized air. In this manner, the selective aftward injection of highspeed mass flows of pressurized air from yaw effectors 340 generates yawcontrol moments during hover.

Even though aircraft 10 has been described and depicted as having anactive flow control system that controls high speed mass flow injectionsof pressurized air to the lift fan injector system, the pitch effectorsystem, the roll effector system and the yaw effector system toinfluence lift coefficients, generate control moments and generatethrust vectors, it should be understood by those having ordinary skillin the art that pitch, roll and yaw authority in certain flight modescould alternatively or additionally be provided using mechanicaldeflectors such as ailerons, elevators, rudders, flaps or otheraerodynamic surfaces. For example, pitch control authority could beachieved by collectively shifting upper expansion ramp 112 and lowerexpansion ramp 114 of thruster nozzle 42 to direct propulsive gas 124upward and downward to generate pitch control moments.

Referring next to FIGS. 6A-6F in the drawings, various views of afan-in-wing blended wing body aircraft 400 operable to transitionbetween thrust-borne lift in a VTOL orientation and wing-borne lift in aforward flight orientation are depicted. FIGS. 6A, 6C and 6E depictaircraft 400 in the VTOL orientation wherein a lift fan system providesthrust-borne lift to the aircraft. FIGS. 6B, 6D and 6F depict aircraft400 in the forward flight orientation wherein a forced air bypass systemprovides bypass air that combines with engine exhaust to generateforward thrust with the forward airspeed of aircraft 400 providingwing-borne lift enabling aircraft 400 to have a high speed, highendurance, low observable forward flight mode. Aircraft 400 shares manycommon elements with aircraft 10 with the exception that the blendedwing body airframe 402 of aircraft 400 has a rhombus shaped body withoutthe winglets of aircraft 10. Similar to aircraft 10 and with referenceto FIGS. 1H-1G, aircraft 400 has a lift fan system including lift fans22 a, 22 b in a tandem lateral orientation, butterfly doors 24 a, 24 b,louvers 26 a, 26 b, rotor assemblies 28 a, 28 b, a turboshaft engine 30and a transmission 32. Aircraft 400 also has a forced air bypass systemthat includes inlets 34 a, 34 b, bypass fans 36 a, 36 b and bypass ducts38 a, 38 b that are coupled to an exhaust system 40 configured with athruster nozzle 42.

Referring also to FIGS. 2A, 3A, 4A and 5A, aircraft 400 has an activeflow control system that includes an active flow control module 54executed by flight control system 44, engine 30 and compressor 46 aswell as manifold systems, valve systems and controller systems thatregulate the flow of high pressure air to the lift fan injector systemincluding lift fan injectors 60 a, 60 b, the pitch effector systemincluding pitch effector 48, the roll effector system including rolleffectors 50 a, 50 b and the yaw effector system including yaw effectors52 a, 52 b. The active flow control system controls the selective highspeed mass flow injections of pressurized air that influence liftcoefficients, generate control moments and generate thrust vectors foraircraft 400 during VTOL, forward and transition flight modes, asdiscussed herein.

Certain flight control operations of aircraft 400 are substantiallysimilar to that of aircraft 10. For example, pitch control authority inVTOL mode, forward flight mode and transition modes is provided by pitcheffector 48. Roll control authority in VTOL mode is provided by liftfans 22 a, 22 b. Roll control authority in forward flight mode isprovided by roll effectors 50 a, 50 b. Roll control authority intransition modes is provided by lift fans 22 a, 22 b and/or rolleffectors 50 a, 50 b. Yaw control authority in VTOL and transition modesis provided by lift fans 22 a, 22 b and/or yaw effectors 52 a, 52 b. Yawcontrol authority in forward flight mode is provided by yaw effectors 52a, 52 b. Translation authority in VTOL mode is provided by lift fans 22a, 22 b.

Referring next to FIGS. 7A-7I in the drawings, various views of afan-in-wing blended wing body aircraft 500 operable to transitionbetween thrust-borne lift in a VTOL orientation and wing-borne lift in aforward flight orientation are depicted. FIGS. 7A, 7C and 7E depictaircraft 500 in the VTOL orientation wherein a lift fan system providesthrust-borne lift to the aircraft. FIGS. 7B, 7D and 7F depict aircraft500 in the forward flight orientation wherein a forced air bypass systemprovides bypass air that combines with engine exhaust to generateforward thrust with the forward airspeed of aircraft 500 providingwing-borne lift enabling aircraft 500 to have a high speed, highendurance, low observable forward flight mode. Aircraft 500 shares manycommon elements with aircraft 10 with the exception that the blendedwing body airframe 502 of aircraft 500 has a kite shaped body withoutthe winglets of aircraft 10 and aircraft 500 has a lift fan system withthree lift fans. Specifically, the lift fan system of aircraft 500includes lift fans 22 a, 22 b, 22 c in a tandem lateral and forwardorientation, butterfly doors 24 a, 24 b, 24 c, louvers 26 a, 26 b, 26 c,rotor assemblies 28 a, 28 b, 28 c, turboshaft engine 30 and transmission32. In the illustrated embodiment, rotor assemblies 28 a, 28 b aredepicted as having a single rotor system while rotor assembly 28 c isdepicted as having a coaxial rotor system with two counter-rotatingrotor assemblies. Aircraft 500 also has a forced air bypass system thatincludes inlets 34 a, 34 b, bypass fans 36 a, 36 b and bypass ducts 38a, 38 b that are coupled to an exhaust system 40 configured with athruster nozzle 42.

Similar to aircraft 10, aircraft 500 has an active flow control systemthat includes an active flow control module 54 executed by flightcontrol system 44, engine 30 and compressor 46 as well as manifoldsystems, valve systems and controller systems (see also FIGS. 2A, 3A, 4Aand 5A) that regulate the flow of high pressure air to the lift faninjector system, the pitch effector system including pitch effector 48,the roll effector system including roll effectors 50 a, 50 b and the yaweffector system including yaw effectors 52 a, 52 b. The active flowcontrol system controls the selective high speed mass flow injections ofpressurized air that influence lift coefficients, generate controlmoments and generate thrust vectors for aircraft 500 during VTOL,forward and transition flight modes, as discussed herein.

Certain flight control operations of aircraft 500 will now be described.Pitch control authority in VTOL mode is provided by lift fan 22 c. Pitchcontrol authority in forward flight mode is provided by pitch effector48. Pitch authority in transition modes is provided by lift fan 22 cand/or pitch effector 48. Roll control authority in VTOL mode isprovided by lift fans 22 a, 22 b. Roll control authority in forwardflight mode is provided by roll effectors 50 a, 50 b. Roll controlauthority in transition modes is provided by lift fans 22 a, 22 b and/orroll effectors 50 a, 50 b. Yaw control authority in VTOL and transitionmodes is provided by lift fans 22 a, 22 b, 22 c and/or yaw effectors 52a, 52 b. Yaw control authority in forward flight mode is provided by yaweffectors 52 a, 52 b. Translation authority in VTOL mode is provided bylift fans 22 a, 22 b, 22 c.

Referring next to FIGS. 8A-8F in the drawings, various views of afan-in-wing blended wing body aircraft 600 operable to transitionbetween thrust-borne lift in a VTOL orientation and wing-borne lift in aforward flight orientation are depicted. FIGS. 8A, 8C and 8E depictaircraft 600 in the VTOL orientation wherein a lift fan system providesthrust-borne lift to the aircraft. FIGS. 8B, 8D and 8F depict aircraft600 in the forward flight orientation wherein a forced air bypass systemprovides bypass air that combines with engine exhaust to generateforward thrust with the forward airspeed of aircraft 600 providingwing-borne lift enabling aircraft 600 to have a high speed, highendurance, low observable forward flight mode. Aircraft 600 shares manycommon elements with aircraft 500 with the exception that the blendedwing body airframe 602 of aircraft 600 has a kite shaped body withwinglets 604 a, 604 b. Aircraft 600 has a lift fan system including liftfans 22 a, 22 b, 22 c in a tandem lateral and forward orientation,butterfly doors 24 a, 24 b, 24 c, louvers 26 a, 26 b, 26 c, rotorassemblies 28 a, 28 b, 28 c, turboshaft engine 30 and transmission 32(see also FIGS. 7G-7I). Aircraft 600 also has a forced air bypass systemthat includes inlets 34 a, 34 b, bypass fans 36 a, 36 b and bypass ducts38 a, 38 b that are coupled to an exhaust system 40 configured with athruster nozzle 42.

Aircraft 600 has an active flow control system that includes an activeflow control module 54 executed by flight control system 44, engine 30and compressor 46 as well as manifold systems, valve systems andcontroller systems (see also FIGS. 2A, 3A, 4A and 5A) that regulate theflow of high pressure air to the lift fan injector system, the pitcheffector system including pitch effector 48, the roll effector systemincluding roll effectors 50 a, 50 b and the yaw effector systemincluding yaw effectors 52 a, 52 b. The active flow control systemcontrols the selective high speed mass flow injections of pressurizedair that influence lift coefficients, generate control moments andgenerate thrust vectors for aircraft 600 during VTOL, forward andtransition flight modes, as discussed herein.

Certain flight control operations of aircraft 600 will now be described.Pitch control authority in VTOL mode is provided by lift fan 22 c. Pitchcontrol authority in forward flight mode is provided by pitch effector48. Pitch authority in transition modes is provided by lift fan 22 cand/or pitch effector 48. Roll control authority in VTOL mode isprovided by lift fans 22 a, 22 b. Roll control authority in forwardflight mode is provided by roll effectors 50 a, 50 b. Roll controlauthority in transition modes is provided by lift fans 22 a, 22 b and/orroll effectors 50 a, 50 b. Yaw control authority in VTOL and transitionmodes is provided by lift fans 22 a, 22 b, 22 c and/or yaw effectors 52a, 52 b. Yaw control authority in forward flight mode is provided by yaweffectors 52 a, 52 b. Translation authority in VTOL mode is provided bylift fans 22 a, 22 b, 22 c.

Referring next to FIGS. 9A-9I in the drawings, various views of afan-in-wing blended wing body aircraft 700 operable to transitionbetween thrust-borne lift in a VTOL orientation and wing-borne lift in aforward flight orientation are depicted. FIGS. 9A, 9C and 9E depictaircraft 700 in the VTOL orientation wherein a lift fan system providesthrust-borne lift to the aircraft. FIGS. 9B, 9D and 9F depict aircraft700 in the forward flight orientation wherein a forced air bypass systemprovides bypass air that combines with engine exhaust to generateforward thrust with the forward airspeed of aircraft 700 providingwing-borne lift enabling aircraft 700 to have a high speed, highendurance, low observable forward flight mode. Aircraft 700 shares manycommon elements with aircraft 10 with the exceptions that the blendedwing body airframe 702 of aircraft 700 has a kite shaped body withforward winglets 704 a, 704 b, aircraft 700 has a lift fan system withlift fans in a tandem longitudinal orientation and aircraft 700 has abinary engine system. Specifically, the lift fan system of aircraft 700includes lift fans 22 c, 22 d in a tandem longitudinal orientation,butterfly doors 24 c, 24 d, louvers 26 c, 26 d, rotor assemblies 28 c,28 d, turboshaft engines 30 a, 30 b and transmission 32. Aircraft 700also has a forced air bypass system that includes inlets 34 c, 34 d,bypass fans 36 c, 36 d, 36 e, 36 f and bypass ducts 38 c, 38 d, 38 e, 38f that are coupled to exhaust systems 40 a, 40 b configured withthruster nozzles 42 a, 42 b.

Similar to aircraft 10, aircraft 700 has an active flow control systemthat includes an active flow control module 54 executed by flightcontrol system 44, engine 30 and compressor 46 as well as manifoldsystems, valve systems and controller systems (see also FIGS. 2A, 3A, 4Aand 5A) that regulate the flow of high pressure air to the lift faninjector system, the pitch effector system including pitch effectors 48a, 48 b, the roll effector system including roll effectors 50 a, 50 band the yaw effector system including yaw effectors 52 a, 52 b. Theactive flow control system controls the selective high speed mass flowinjections of pressurized air that influence lift coefficients, generatecontrol moments and generate thrust vectors for aircraft 700 duringVTOL, forward and transition flight modes, as discussed herein.

Certain flight control operations of aircraft 700 will now be described.Pitch control authority in VTOL mode is provided by lift fans 22 c, 22d. Pitch control authority in forward flight mode is provided by pitcheffectors 48 a, 48 b. Pitch authority in transition modes is provided bylift fans 22 c, 22 d and/or pitch effectors 48 a, 48 b. Roll controlauthority in VTOL mode is provided by yaw effectors 52 a, 52 b acting asroll effectors. Roll control authority in forward flight and transitionmodes is provided by roll effectors 50 a, 50 b. Yaw control authority inVTOL mode is provided by lift fans 22 c, 22 d. Yaw control authority inforward flight mode is provided by yaw effectors 52 a, 52 b. Yaw controlauthority in transition modes is provided by lift fans 22 c, 22 d and/oryaw effectors 52 a, 52 b. Translation authority in VTOL mode is providedby lift fans 22 c, 22 d.

Referring next to FIGS. 10A-10I in the drawings, various views of afan-in-wing blended wing body aircraft 800 operable to transitionbetween thrust-borne lift in a VTOL orientation and wing-borne lift in aforward flight orientation are depicted. FIGS. 10A, 10C and 10E depictaircraft 800 in the VTOL orientation wherein a lift fan system providesthrust-borne lift to the aircraft. FIGS. 10B, 10D and 10F depictaircraft 800 in the forward flight orientation wherein a forced airbypass system provides bypass air that combines with engine exhaust togenerate forward thrust with the forward airspeed of aircraft 800providing wing-borne lift enabling aircraft 800 to have a high speed,high endurance, low observable forward flight mode. Aircraft 800 sharesmany common elements with aircraft 10 with the exceptions that theblended wing body airframe 802 of aircraft 800 has a kite shaped bodywith forward winglets 804 a, 804 b, and aircraft 800 has a lift fansystem with a unitary lift fan. Specifically, the lift fan system ofaircraft 800 includes a single lift fan 22 e, butterfly doors 24 e,louvers 26 e, a rotor assembly 28 e, turboshaft engine 30 andtransmission 32. In the illustrated embodiment, rotor assembly 28 e isdepicted as having a coaxial rotor system with two counter-rotatingrotor assemblies. Aircraft 800 also has a forced air bypass system thatincludes inlets 34 a, 34 b, bypass fans 36 a, 36 b and bypass ducts 38a, 38 b that are coupled to exhaust system 40 configured with thrusternozzle 42.

Similar to aircraft 10, aircraft 800 has an active flow control systemthat includes an active flow control module 54 executed by flightcontrol system 44, engine 30 and compressor 46 as well as manifoldsystems, valve systems and controller systems (see also FIGS. 2A, 3A, 4Aand 5A) that regulate the flow of high pressure air to the lift faninjector system, the pitch effector system including pitch effector 48,the roll effector system including roll effectors 50 a, 50 b and the yaweffector system including yaw effectors 52 a, 52 b. The active flowcontrol system controls the selective high speed mass flow injections ofpressurized air that influence lift coefficients, generate controlmoments and generate thrust vectors for aircraft 800 during VTOL,forward and transition flight modes, as discussed herein.

Certain flight control operations of aircraft 800 will now be described.Pitch control authority in VTOL mode, forward flight mode and transitionmodes is provided by pitch effector 48. Roll control authority in VTOLmode is provided by yaw effectors 52 a, 52 b acting as roll effectors.Roll control authority in forward flight and transition modes isprovided by roll effectors 50 a, 50 b. Yaw control authority in VTOLmode and transition modes is provided by differential operations for thecoaxial rotor system of lift fan 22 e and/or yaw effectors 52 a, 52 b.Yaw control authority in forward flight mode is provided by yaweffectors 52 a, 52 b. Translation authority in VTOL mode is provided bylift fans 22 e.

The foregoing description of embodiments of the disclosure has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the embodimentswithout departing from the scope of the present disclosure. Suchmodifications and combinations of the illustrative embodiments as wellas other embodiments will be apparent to persons skilled in the art uponreference to the description. It is, therefore, intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. An aircraft operable to transition betweenthrust-borne lift in a VTOL orientation and wing-borne lift in a forwardflight orientation, the aircraft comprising: a blended wing body; firstand second engines disposed within the body, the engines having aturboshaft mode and a turbofan mode, the engines configured to generateengine exhaust; a binary lift fan system disposed within the body, thelift fan system including ducted fans in a tandem longitudinalconfiguration along a central longitudinal axis of the body; first andsecond forced air bypass systems disposed within the body, the forcedair bypass systems configured to generate bypass air; and a firstexhaust system coupled to the first engine and the first forced airbypass system and a second exhaust system coupled to the second engineand the second forced air bypass system; wherein, in the VTOLorientation, the first and second engines are in the turboshaft modecoupled to the lift fan system such that the first and second enginesprovide rotational energy to the ducted fans generating the thrust-bornelift; and wherein, in the forward flight orientation, the first andsecond engines are in the turbofan mode coupled to the first and secondforced air bypass systems such that the bypass air combines with theengine exhaust in the respective first and second exhaust systems toprovide forward thrust generating the wing-borne lift.
 2. The aircraftas recited in claim 1 wherein the blended wing body further comprises afuselage and a wing.
 3. The aircraft as recited in claim 1 wherein theblended wing body further comprises a kite shaped body with forwardwinglets.
 4. The aircraft as recited in claim 1 wherein each of theducted fans further comprises a rotor assembly having a plurality ofvariable pitch rotor blades.
 5. The aircraft as recited in claim 1wherein the tandem longitudinal orientation of the ducted fans isconfigured to generate pitch control moments in the VTOL orientation. 6.The aircraft as recited in claim 1 wherein each forced air bypass systemfurther comprises an inlet, a bypass fan disposed within the bodydownstream of the inlet and a bypass duct disposed within the bodydownstream of the bypass fan, the bypass duct coupled to the exhaustsystem.
 7. The aircraft as recited in claim 6 wherein each inlet furthercomprises an air inlet on an upper surface of the body.
 8. The aircraftas recited in claim 1 wherein each exhaust system further comprises afilm cooled nozzle.
 9. The aircraft as recited in claim 1 furthercomprising a transmission disposed between the engines and the lift fansystem, the transmission engaging the engines with the lift fan systemwhen the engines are in the turboshaft mode and disengaging the enginesfrom the lift fan system when the engines are in the turbofan mode. 10.The aircraft as recited in claim 1 further comprising a transmissiondisposed between the engines and the forced air bypass systems, thetransmission engaging the engines with the forced air bypass systemswhen the engines are in the turbofan mode and disengaging the enginesfrom the forced air bypass systems when the engines are in theturboshaft mode.
 11. The aircraft as recited in claim 1 wherein, in theforward flight orientation, the forced air bypass systems are configuredto generate a bypass ratio of between 8 to 1 and 12 to
 1. 12. Theaircraft as recited in claim 1 further comprising an active flow controlsystem configured to generate control moments in the VTOL orientationand the forward flight orientation.
 13. The aircraft as recited in claim12 wherein at least a portion of the active flow control system isintegral with the binary lift fan system.
 14. The aircraft as recited inclaim 12 wherein at least a portion of the active flow control system isintegral with the exhaust systems.
 15. The aircraft as recited in claim12 wherein the active flow control system further comprises pitcheffectors configured to generate pitch control moments in the forwardflight orientation.
 16. The aircraft as recited in claim 12 wherein theactive flow control system further comprises roll effectors configuredto generate roll control moments in the forward flight orientation. 17.The aircraft as recited in claim 12 wherein the active flow controlsystem further comprises roll effectors configured to generate rollcontrol moments in the VTOL flight orientation.
 18. The aircraft asrecited in claim 12 wherein the active flow control system furthercomprises yaw effectors configured to generate yaw control moments inthe forward flight orientation.
 19. The aircraft as recited in claim 12wherein the active flow control system further comprises yaw effectorsconfigured to generate yaw control moments in the VTOL flightorientation.
 20. An aircraft operable to transition between thrust-bornelift in a VTOL orientation and wing-borne lift in a forward flightorientation, the aircraft comprising: a blended wing body; first andsecond engines disposed within the body, the engines having a turboshaftmode and a turbofan mode, the engines configured to generate engineexhaust; a binary lift fan system disposed within the body, the lift fansystem including ducted fans in a tandem longitudinal configurationalong a central longitudinal axis of the body, the binary lift fansystem configured to generate pitch control moments in the VTOLorientation; first and second forced air bypass systems disposed withinthe body, the forced air bypass systems configured to generate bypassair; a first exhaust system coupled to the first engine and the firstforced air bypass system and a second exhaust system coupled to thesecond engine and the second forced air bypass system; and an activeflow control system configured to generate roll and yaw control momentsin the VTOL orientation and pitch, roll and yaw control moments in theforward flight orientation; wherein, in the VTOL orientation, the firstand second engines are in the turboshaft mode coupled to the lift fansystem such that the first and second engines provide rotational energyto the ducted fans generating the thrust-borne lift; and wherein, in theforward flight orientation, the first and second engines are in theturbofan mode coupled to the first and second forced air bypass systemssuch that the bypass air combines with the engine exhaust in therespective first and second exhaust systems to provide forward thrustgenerating the wing-borne lift.